Electric heating unit



Sept. 9, 1958 c PEARCE 2,851,571

' ELECTRIC HEATING UNIT Filed NOV. 23, 1954 2 Sheets-Sheet l Fig. 2

INVENTOR. BY Geoge C Pearce His Affomey Sept. 9, 1958 e. c. PEARCE 2,351,571

ELECTRIC HEATING UNIT Filed Nov. 23, 1954 2 Sheets-Sheet 2 mramozz rge 6. Fe arce His Afforney marsh Patented Sept. 9, 1958 ice United States ELECTRIC HEATING UNIT George C. Pearce, Dayton, Ohio, assignor'to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application November 23, 1954, Serial No. 470,581

1 Claim. (Cl. 201-67) This invention relates to electrical apparatus and more particularly to sheathed electric heaters for low tempera ture heating.

Electric heaters for low temperatures are used for various purposes such as defrosting refrigerant evaporators.

It is an object of this invention to provide a durable low cost sheathed electric heater which can be readily manufactured.

It is another object of this invention to provide a simple low cost method of making a sheathed electric heater for low temperatures.

These and other objects are obtained in the forms shown in the drawings in which a metal carrier is provided with a double threaded groove. Two ends of an electrical conductor are wrapped side by side in the adjacent grooves. This assembly is slipped into the tubular sheath and the ends are plugged after which the tubular sheath is swaged tightly into contact with the metal carrier to compact the heaters in the carrier. The assembly may fit in aligned apertures provided in a refrigerant evapoator or may be placed anywhere where heating is desired within the limits of the electrical insulation of the heaters.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred form of the invention is clearly shown.

In the drawings:

Figure l is a sectional view of a refrigerant evaporator disclosing a sheathed electric heater employing one form of any invention;

Figure 2 is a fragmentary sectional view showing a modified end construction for the heater;

Figure 3 is a fragmentary view showing the method of providing parallel helical grooves in a metal carrier;

Figure 4 is a fragmentary view showing the method of winding two insulated heater conductors simultaneously in the groove;

Figure 5 is a fragmentary view showing insertion of the metal carrier with the heater conductors in the grooves into the tubular sheath; and

Figure 6 is a frgamentary view showing the swaging of the plugged tubular sheath firmly into contact with the outer surfaces of the metal carrier.

Referring now to the drawings and more particularly to Figure 1 there is shown a refrigerant evaporator including refrigerating tubing of evaporator including refrigerant tubing 22 extending back and forth in serpentine fashion through the metal cross-fins 24. Such refrigerant evaporators often operate at temperatures below 32. This often causes accumulation of frost upon the tubes 22 and sometimes upon the fins 24. One of the forms of removing this frost is by the use of low temperature electric heaters.

According to my invention for this purpose I provide the form of sheath tubular electric heater 26 disclosed herein. This heater includes a metal carrier 28 provided with parallel helical grooves 30 and 32 which extend side by side throughout the length of the metal carrier. Lodged in these grooves is an insulated heater conductor 34-. The two ends 36 and 38 of the heater conductor extend through spaced axially extending holes in a synthetic rubber plug 4% which may be of Buna N or silicone rubber. The two sections of the conductors 34 may be joined as indicated by the reference character 42 or this may be a single continuous conductor. The heater conductor 34 is preferably provided with electrical insulation preferably class B electrical insulation such as silicone rubber or spun glass fibers. A tubular sheath 44 surrounds the metal carrier 28 and is plugged at the one end by the synthetic rubber plug 40 and at the opposite end by a synthetic rubber plug 46 of similar material. The tubular metal sheath 44 swages down tightly into contact with the metal carrier 28 to firmly hold the rubber plugs 40 and 46 and to tightly engage the metal carrier 28 so that the insulated heater conductors are firmly held in the grooves. This provides a suflicient heater construction in which the heat generated in the heater conductor passes through the insulated material and the tubular sheath 44 directly to the cross fins 24 which firmly fit the outer surface of the tubular sheath 44. The metal carrier 28 and the tubular sheath 44 may be made of excellent conducting metal such as copper or aluminum.

In Figure 2 is shown a modified form of construction in which the tubular sheath 144 is provided with a closed end 146 and the insulated heater conductor 134 is shown as being formed of a single section of insulated conductor wire with a looped portion 135 providing the comlection between the sections in the two helical grooves.

The heater is made as follows: the metal carrier 28 is turned in a lathed type machine and provided with the parallel cutting tools 230 and 232 which are moved progressively to the right as the metal carrier 28 is being turned as shown in Figure 3. In Figure 4 is illustrated the next step in which the metal carrier 28 is rotated while the two conductor sections 34a and 34b are wound simultaneously as the carrier 28 is rotated. The winding of the sections is begun at the right end where the ends of the heater conductors are joined. Following the wrapping of the heater conductor sections 34a and 34b in the grooves the metal carrier with the heater conductors that is the metal carrier 28 with the metal conductors 34a and 34b are inserted in the tubular sheath 44 by a telescoping action as is shown in Figure 5. The ends of the tubular sheath 44 are then plugged by the plugs 40 and 46 of synthetic rubber with the heater conductor ends 36 and 38 being threaded through the parallel holes in the plug 40 as shown in Figure l. The assembled heater is then passed through a swaging machine which swages the tubular sheath down tightly upon the plugs and the metal core 28 in the manner illustrated in Figure 6.

This method of manufacture makes it possible to produce this heater rapidly at a relatively low cost.

. While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted as may come within the scope of the claim which follows.

What is claimed is as follows:

An electric heating unit including a solid non-ferrous metal carrier provided with two continuous grooves extending side by side upon its surface, an electric wire heater enclosed in high temperature non-metallic resilient electrical insulation extending in series through each of the grooves, and a metal sleeve tightly enclosing and gripping said carrier between each groove and also enclosing and contacting said heater holding the heater in said which extend said terminal. portions, said'plug being tightly held in sealing engagement within: the end ofsaidl sleeves and being tightly gripped by' said-sleeve;

References Cited in the file of this patent UNITED STATES PATENTS Abbott Aug. 24, 1920 Lederer July 3, 1945 Trilling et a1. Jan. 4, 1949 Charbonneau et a1 Nov. 29, 1949 

